1. Field of the Invention
The present invention relates to an improved process for compounding nitrile polymers with a formaldehyde compound in order to reduce the extractable HCN content of packaging materials made from the nitrile polymer.
2. Description of the Prior Art
In recent years it has been discovered that certain polymeric nitrile resins are especially suitable for packaging applications because of their excellent water and oxygen barrier properties. Such polymers are described at length in U.S. Pat. Nos. 3,451,538 and 3,615,710, among others. Even more recently it has been discovered that although such nitrile polymers have excellent barrier properties they may be unsuitable for certain packaging applications because they contain trace, though detectable, amounts of hydrogen cyanide (HCN) which may be extracted by and impart a taste to the contents of the package.
The amount of HCN in such nitrile polymers will vary with the nitrile monomer, the total nitrile content of the polymer, the polymerization method used to prepare the polymer, the processing and thermal history of the polymer and other factors. Moreover, it has been found that the amount of extractable HCN in nitrile polymers may be increased after the polymer has been subjected to forming operations wherein the polymer has been heated in order to soften and/or melt the polymer prior to forming it into shaped articles.
The trace amount of extractable HCN present in such nitrile packaging materials is very low and presents no known health or safety problems. In fact, the amount of extractable HCN in such nitrile polymers is lower than that found in many foods. In this regard it should be noted that HCN is a natural component in many foods and many other foods such as cereals, cocoa, ham, bacon and sausage, which are fumigated with HCN (prussic acid), are permitted to contain from 50 to 200 parts per million of HCN. (See the Food Additive Regulations of the FDA (page 3, Subpart D, Paragraph 121, 1072) as published in the Federal Register: Dec. 23, 1965; 30 F.R. 0.15912 and the 1962 Public Health Service Publication 956 "Drinking Water Standards".).
However, as stated above, the HCN in certain nitrile packaging materials may, in certain instances, be extracted and impart a taste to the contents of the package. The problem of HCN extraction as it affects taste, is of concern in the packaging of beverages which are in prolonged intimate contact with the container. In these packaging applications the probability of HCN extraction is very high.
Recently, it has been discovered that the extractable HCN content of packaging materials prepared from high nitrile polymers can be reduced by compounding the nitrile polymer with a formaldehyde compound prior to the fabrication of the packaging material as is disclosed in U.S. Pat. application Ser. No. 323,771, filed Jan. 15, 1973 and now U.S. Pat. No. 3,870,802 . However, even more recently it has been discovered that in certain instances excess formaldehyde may remain in the packaging material. For certain food packaging applications, it may be desirable to reduce the level of extractable formaldehyde to less than 200 parts per billion.
The present invention discloses an improved method for compounding a high nitrile polymer with a formaldehyde compound in order to reduce the extractable HCN content of packaging materials prepared from the nitrile polymer, while maintaining the extractable formaldehyde content below certain levels.